The present invention relates to digital signal processing techniques in a broad sense, and particularly relates to a method for managing audio data and sub-Q data in equipment capable of receiving a digital audio from the outside and a method for outputting such data.
In a music CD, sub-Q data which is different data from audio data is recorded in a sub-coded Q channel. Such sub-Q data is used for reproduction time display and pause detection in dubbing. Conventionally, a system in which in reproducing a music CD, audio data and sub-Q data are synchronized and then output has been known (see Japanese Laid-Open Patent Publication No. 2001-155432).
In recent years, equipment capable of handling not only optical disc reproduction but also external digital audio input has been widely spread. Digital audio from the outside is received in the format defined in IEC 60958 or IEC 61937. When some audio processing is performed to the received data, audio data has to be extracted from an IEC format. In the IEC format, besides audio data, auxiliary information such as a channel status and user data is added. When such information is used for reproduction, the auxiliary information has to be extracted with the audio data. The extracted audio data and the extracted auxiliary data are managed in different buffers, respectively. When the extracted audio data and the auxiliary data are internally processed and then are output in the IEC format again, extracted and separated data have to be encoded.
When sub-Q data contained in user data is processed in receiving digital audio from the outside, a reproduction state of connected equipment is not known by receiver equipment, the receiver equipment has to be operated in a sub-Q input mode at all the time. However, when data from some other media than a music CD is being reproduced by connected equipment, sub-Q data does not exist in user data. When the music CD is reproduced, a music CD definitely contains sub-Q data and, therefore, there arises no problem. When data from the outside is received, however, the case where sub-Q data is not received has to be taken into consideration so that the occurrence of a problem such as sound deterioration can be avoided even in such case. Once audio data and auxiliary information are separated from each other, a timing difference is generated. Accordingly, it is difficult to precisely synchronize between the audio data and the auxiliary data and then output the synchronized data in the IEC format again. Therefore, when an output of the audio player is used with some external equipment connected thereto for the purpose of dubbing, track management might be wrongly performed in the external equipment.
In the above-described known system, when sub-Q data in user data is processed in receiving digital audio from the outside, it is highly possible that sound deterioration occurs. Moreover, audio data and sub-Q data are once separated from each other to perform audio processing, so that even if the audio data and sub-Q data are encoded again in an output stage, a timing difference is generated. Therefore, in the known system, when the audio player is used for dubbing of a music CD, a problem in which a detection point between tracks varies in receiver equipment arises.